Heterochromatin is one of the most dynamic components in the genome of species. Previous studies on the heterochromatin content and distribution in Heteroptera (insects with holokinetic chromosomes) have shown that the species belonging to the family Coreidae are interesting model organisms since they show very diverse C bands patterns. In the present work, we analyzed the C-band pattern in individuals of Holhymenia rubiginosa from different populations collected in different years. This species has the diploid karyotype 2n = 27/28 = 24 + 2m + X0/XX (male/female). C-bands are terminally, subterminally or interstitially located on 10-17 chromosomes and a remarkable heterochromatin heteromorphism is observed in the meiotic bivalents: in the presence/absence of bands, in the size of bands and number of bands. A heteromorphism is also inferred in the number of ribosomal genes from the difference in the fluorescent in situ hybridization signals between NOR-homologues. Chiasmata are generally located opposite to conspicuous C-bands, but in some bivalents chiasmata are also observed in close proximity to C-bands. Considering the striking variation in heterochromatin content between individuals and populations it is suggested that heterochromatin should be selectively neutral in H. rubiginosa.
The Coreidae (Heteroptera) have holokinetic chromosomes and during male meiosis the autosomal bivalents segregate reductionally at anaphase I while the sex chromosomes do so equationally. The modal diploid chromosome number of the family is 2n = 21, with a pair of m-chromosomes and an X0/XX sex chromosome system. A 2n = 24/26 (male/female) and an X1X20/X1X1X2X2 sex chromosome system were found in Spartocera batatas (Fabricius). C-banding and fluorescent-banding revealed the presence of AT-rich heterochromatic bands medially located on all the autosomes, and one telomeric band on both the X1 and X2 chromosomes. This banding pattern differed from the telomeric heterochromatin distribution found in most other heteropteran species. The X1 and X2 chromosomes were intimately associated during male meiosis and difficult to recognize as two separate entities. Based on a comparison with the behaviour of sex chromosomes in other coreids and other heteopterans with multiple sex chromosomes it is suggested that the particular behaviour of X1 and X2 chromosomes in coreid species with multiple sex chromosome systems evolved as an alternative mechanism for ensuring the proper segregation of the sex chromosomes during meiosis.